In otl By the late 1960s with Chinese-Soviet border clashes it was obvious that China and the Soviets were at each other's throats. Nixon and Mao took the opportunity to realign China into an American ally. With China now on the side of the US against the Soviets the strategic value of Vietnam and SE Asia plummeted, as the domino theory no longer worked if the major Asian Communist power is siding with capitalist America against Soviet Russia.
What if this happened earlier? The Sino-Soviet split had already happened by the early-mid 1960s. Let's say in 1964 or so some kind of border skirmish is fought between China and the USSR in the Ussuri river region which otl took place 5 years later. Let's say the Chinese leadership, with or without Mao in power, decides to take the rapprochement option with the US. Let's say in ttl President Nixon won 1960 and coasts into re-election in '64.
Does Nixon go to China 8 years earlier then? If so, what does this mean for Vietnam? Does the US even intervene? Does the US win the war in Vietnam if the Chinese either don't back the North Vietnamese or is even pressuring them to come to a peace settlement and wind down the war in the south?